Note: This must become a chapter on array behavior.
Volunteers? - thomas 1998-01-12

Postgres allows attributes of a
class to be defined as variable-length multi-dimensional arrays.
Arrays of any built-in type or user-defined type can be created. To
illustrate their use, we create this class:

The above query will create a class named sal_emp with a text string
(name), a one-dimensional array of int4
(pay_by_quarter), which represents the employee's salary by
quarter, and a two-dimensional array of text (schedule), which represents the employee's
weekly schedule. Now we do some INSERTSs;
note that when appending to an array, we enclose the values within
braces and separate them by commas. If you know C, this is not unlike the syntax for initializing
structures.

We can also access arbitrary slices of an array, or subarrays.
An array slice is denoted by writing "lower subscript : upper
subscript" for one or more array dimensions. This query retrieves
the first item on Bill's schedule for the first two days of the
week:

UPDATE sal_emp SET pay_by_quarter = '{25000,25000,27000,27000}'
WHERE name = 'Carol';

or updated at a single entry:

UPDATE sal_emp SET pay_by_quarter[4] = 15000
WHERE name = 'Bill';

or updated in a slice:

UPDATE sal_emp SET pay_by_quarter[1:2] = '{27000,27000}'
WHERE name = 'Carol';

It is not currently possible to resize an array value except by
complete replacement; for example, we couldn't change a four-
element array value to a five-element value with a single
assignment to array[5].

The syntax for CREATE TABLE allows fixed-length arrays to be
defined:

CREATE TABLE tictactoe (
squares int4[3][3]
);

However, the current implementation does not enforce the
array size limits --- the behavior is the same as for arrays of
unspecified length.